The disclosure of Japanese Patent Application No. 2001-14748 filed on Jan. 23, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a reclining device. More specifically, the invention relates to the fitting of a seat back and a seat cushion.
2. Description of Related Art
A reclining device of a certain type is disclosed, for example, in Japanese Patent Application Laid-Open No. 8-253063. This reclining device comprises a plurality of pawls each having outer teeth on the front end side, an annular ratchet having inner teeth on the inner periphery side, and a holder for holding the pawls such that they can move toward and away from the inner teeth of the ratchet. The reclining device further comprises a cam body that receives the pawls. The cam body presses the pawls forwards so that the pawls are brought into mesh with the ratchet and locked with respect thereto. Upon application of an arbitrary operational force, the cam body is activated and cancels the operation of pressing the pawls against the ratchet so that the pawls are removed from the ratchet and unlocked therefrom.
The reclining device of this type is designed to prevent the ratchet from rotating relative to the holder when the pawls are locked with respect to the ratchet and to allow the ratchet to rotate relative to the holder when the pawls are unlocked from the ratchet. The reclining device of this type is disposed between a rear end portion of a seat cushion and a lower end portion of a seat back, thus constituting a vehicular reclining seat. For example, the reclining device of this type is designed such that the seat back is longitudinally tiltably supported with respect to the seat cushion by mounting the ratchet on the lower end side of the seat back and the holder on the rear end side of the seat cushion.
If a vehicle employing the vehicular reclining seat encounters an accident, an enormous load is applied to the seat back backwards or forwards from a passenger sitting on the seat cushion. That is, if the vehicle encounters a rear-end collision, the passenger sitting on the seat cushion collides against the seat back with an enormous impact so that the seat back is exposed to an enormous load and urged to tilt backwards. If the vehicle encounters a frontal collision, the passenger sitting on the seat cushion is exposed to an enormous ejective force to be on the verge of being thrown forwards. A seat belt for counterbalancing the enormous ejective force applies an enormous load to the seat back and urges the seat back to tilt forwards. Such an enormous load applied to the seat back directly acts on the reclining device for supporting the seat back with respect to the seat cushion. Such an enormous load applied to the reclining device acts in such a manner to bring the pawls out of mesh with the ratchet and may make it impossible for the reclining seat to support the seat back.
Hence, the reclining device constituting the vehicular reclining seat is required to sufficiently endure an enormous load that is applied to the seat back if the vehicle encounters an accident or the like. The reclining device is also required to have such a high durability. To meet such requirements, the reclining device is generally increased in size and robustness with a view to ensuring that the pawls are more securely in mesh with the ratchet. However, the adoption of such measures inevitably leads to an increase in the weight and cost of the reclining device.
To eliminate such a problem, the reclining device proposed by the aforementioned publication is designed such that an impact protrusion portion protruding toward each lateral wall surface of the guide groove of the holder is formed in a circumferential lateral face at the front end of a corresponding one of the pawls. Upon application of an enormous circumferential load from the side of the seat back, the impact protrusion portion of each of the pawls sinks into a corresponding one of the lateral wall surfaces of the guide groove of the holder due to a circumferential movement of the pawl resulting from an enormous circumferential operational force (turning force) applied to the ratchet. The reclining device proposed by the aforementioned publication employs a meshing-state holding means for causing each of the pawls to sink into a corresponding one of the lateral wall surfaces of the guide groove of the holder to prevent the pawls from retreating from the ratchet and to securely maintain the pawls in mesh with the ratchet.
A reclining device according to one exemplary aspect of the invention comprises pawls, a ratchet, a holder, and a cam body. Each of the pawls has first teeth formed in an end portion thereof, first and second leg portions extending in a direction opposite to the first teeth and formed in an end portion on the other side of the end portion where the first teeth are formed, and a low-rigidity portion formed in at least one of the first and second leg portions and demonstrating a lower rigidity than the other portions of the first and second leg portions. The ratchet has second teeth that mesh with the first teeth and can turn within a range where the second teeth are formed so that the first and second teeth can mesh with each other locally variably. The holder has a guide groove that abuts on and holds a lateral face of each of the pawls so that the pawl slidably moves toward and away from the second teeth of the ratchet. The cam body bears at least one of the first and second leg portions of each of the pawls and presses the first teeth of the pawl toward the ratchet so that the first teeth of the pawl are brought into mesh with the second teeth of the ratchet and that the holder and the ratchet are prevented from rotating relative to each other. The cam body brings the first teeth of the pawl out of mesh with the second teeth of the ratchet so that the holder and the ratchet are allowed to rotate relative to each other.